Duplex centrifugal separator



April 25, 1939- R. s. CLARKE 2,156,253

DUPLEX CENTRIFUGAL SEPARATOB Filed Feb. 20, 1950 Patented Apr. 25, 1939UNITED STATES vPATENT OFFICE DUPLEX CENTRIFUGAL SEPARATOR ApplicationFebruary 20, 1930, Serial No. 430,035

` e claims. (ci. zas-17) This invention relates to improvements incentrifugal separators by means of which a iluid can be separated fromimpurities of different specific gravity. While applicable tocentrifugal separators inA general, the invention relates morespecifically to separators for removing foreign matter from aqueoussuspensions of cellulosic material such as wood pulp, ground wood,cotton linters, bagasse, cornstalks, bamboo, or other fibers.Centrifugal separators of this type ordinarily consist of a cylindricaldrum rotatable about its axis. The stock is fed in at one end and flowsalong the drum to the other end over one or more annular rings whichextend inwardly from the drum. The stock flowing through the drum isheld against the wall of the drum by the centrifugal force of rotation.The capacity of a separator of given diameter, that is, the rate atwhich pulp will be passed through the drum and so properly purified, islimited. When the separator is first started up, the first pulp enteringforms a soft mat or lining within the drum, over which flows the pulpstream. This mat combs the fibers in the stream and catches and holdsthe dirt particles which are found therein. The heavier dirt particlesgradually work through the mat toward the drum wall while the mat itselftends to become gradually more compact. If an increase of capacity isattempted by increasing the speed of rotation above the optimum speed,the mat tends to pack rapidly and thus to diminish its capacity forcatching and holding dirt particles from the pulp stream. Thus capacitycannot be increased beyond a certain point by an increase of speed.

According to the invention, the capacity of a separator of givendiameter may be nearly doubled by mounting a second drum within thefirst, suillcient clearance being provided between the walls of the twodrums for a stream of pulp to ow along the wall of the outer drum. Asecond stream is introduced into the inner drum and flows along the drumto the discharge end where the streams from both drums may be dischargedinto a common receiving channel or into separate receivers. 'Ihisincrease in capacity involves no additional required floor space so thata separator embodying the invention is especially advantageous whereavailable door space is limited. As the diameters of the two drumspreferably do not greatly differ, a speed of rotation which is justsufilcient for the eifective operation of the Linner drum is suitablefor satisfactory operation of the outer drum also. According to theinvention. more than two concentric drums to the fact that the drumsmust be spaced from one another, and if the difference between thediameter of the innermost drum and that of the outermost drum is toogreat, the difference between the centrifugal forces acting in thesedrums will be too great for satisfactory operation.

For a more complete understanding of the invention, reference may be hadto the following description thereof and to the illustration thereof onthe drawing, of which,-

Figure 1 is an elevation of an embodiment of the invention, a portionbeing broken away to show the working parts in section.

Figure 21s a plan'view of the mechanism shown in Figure 1, this ligurebeing drawn to a smaller scale.

Figure 3 is a fragmentary sectional view of a portion of Figure l, drawnto a larger scale, and showing the course of the streams of pulp passingtherethrough.

The embodiment of the invention illustrated on the drawing comprises arotatable drum I0 within which is-mounted an inner drum I I, the drumsbeing coaxial and radially spaced. These drums are mounted by suitableframework on a shaft l2 to which is coupled a suitable motor vI 3 orother equivalent source of power. 0n the drawing the shaft I2 is shownin a vertical position with the 1 motor attached to the lower end. Thisarrangement is merely illustrative and the invention ls not to belimited thereto. At the lower end of the drum I0 an inwardly extendingflange I4 is provided, an open frame I5 being provided to con- -nectthis end of the drum rigidly with the corresponding end of the drum II.The lower end of the drum II is secured to a conical supporting member.I6 having a series of suitable openings I1 through which the' interiorof the drum may be washed when the mechanism is stopped. As shown, thesupporting member I6 is mounted on the upper end of the shaft I2.approximately flush with the upper ends of the drums I 0 and l I. Themember i6 extends downwardly in conical shape and ares outwardly toreach the lower end of the drum II to which it is secured. This openstructure provides space for the insertion of a feed pipe I8 thereabovethrough which pulp stock or other liquid to be purified may be` fed intothe lower portion of the drum Il. The

flange I4 of the drum I0 may extend lower than the end of the drum II toreceive pulp stock through a feed pipe I9.

Within each of the drums I0 and II are one or more rings 20 and 2|.These rings extend inwardly from the shells of the respective drums andserve as barriers over which the pulp stock must iiow in its upwardcourse from the lower ends of the drums. At the upper end of the drumIll an enlarged poriton 22 may be provided having an inwardly extendinglip 23. In vlike manner the drum I I is provided with an enlargedportion 24 having an inwardly extending lip 25 at its upper extremity. Askimming ring 2B is provided for the drum I0, this ring beingconveniently mounted on the exterior of the drum I I and extendingradially outward into the stream of pulp stock owing along the shell ofthe drum III. In like manner a skimming ring 2I is mounted within thedrum II and projects radially toward the enlarged portion 24 of the drumII, so that its outer edge is immersed in a stream of pulp stock in theenlarged portion 24 during the operation of the mechanism. The skimmingrings 26 and 21 are preferably adjustable up and down so as to vary theclearances 28 and 29 respectively between the rings and the ends of theadjacent lips 23 and 25.

The drums are surrounded by a suitable housing 30, the upper portion ofwhich is formed in the shape of a suitable channel 3| to receive pulpstock which flows over the lips 23 and 25. In order to avoidinterference between the streams of pulp discharged into the channel 3l,the lip 25 may be extended slightly above the lip 23, as shown inFigures 1 and 3. The pulp received in the channel 3l may be led olf byany suitable discharge pipe 32.

When operating the mechanism, the motor I3 is started Yto rotate thedrums I and I I at a suitable speed, this speed depending on the averageaverage diameter of the drums` When the drums have been brought up tospeed, pulp stock is admitted through :the supply pipes I8 and I9, the

rate of supply for each drum depending on the diameter thereof. Thestreams of incoming stock are forced against the respective drums bycentrifugal force and form pools below the ring 20 until the depth ofthese pools is sufficient to enable the stock to ow over the respectiverings into the compartments above. The pulp in the pools of stock belowthe rings 20 forms a soft mat which very gradually packs during theoperation of the mechanism. Meanwhile the continued supply of pulp stockflows over the mats below the rings 20, the mats exerting a brushingaction on the flowing stock which tends to straighten out th fibers andto catch particles of knots, sand, or other impurities which havesubstantially the same or greater density than that of the pulp itself.As the stock ows over the rings 20 in thin streams, the edges of therings tend to break up fiber bunches and thus tend to promote a, moreeven distribution of the pulp through the aqueous vehicle. I

I'he lips 25 and 25 are arranged respectively outward a short distanceincomparison with their respective rings 20 so that while the lips act asdams to form pools above the rings 20, the surfaces of these pools areradially outward with respect to the surfaces of the pools below therings 20. The skimming rings 26 and 21, which pro- J'ect outwardlytoward the enlarged portions 22 and 2.4, project beneath the surface ofthe upper pools of stock so that impurities having a lower density thanthe stock are thus carried on the surface of the pools and are caught bythe skimming rings so. that. only the purified middle stratum of stockescapes around the skimming rings and through the clearances 28 and 29between the skimming rings and the respective lips of the drums. Theskimming rings are preferably adjustable to vary the clearances 28 and29 so as to regulate the depth of the upper pools of stock. The depth ofeither pool can be increased by diminishing the clearance between itsskimming ring and the adjacent lip. The sharp edges of the lips 23 and25 have van additional combing effect on the pulp which further breaksup any fiber bunches present in the stock.

s The clearance or spacing between the drums I0 and I I is preferably assmall as possible, consistent with the accommodation of the stream andpool of pulp in the outer drum I0 during the operation of the machine.This minimum clearance is desirable in order not to have too great adifference in the centrifugal forces acting in the respective drums.

Since the drums are of nearly the same size, the capacities of the twoare approximately equal so that the capacity of the mechanism as a wholeis substantially double that of a similar mechanism having but a singledrum of the same diameter.

I claim:

l. Apparatus for purifying pulp stock, which comprises a rotatablevertical shaft, a conical support member secured at its upper end tosaid shaft for rotation therewith and diverging downwardly therefrom, anoutwardly projecting flange at the lower end of said supporting memberhaving apertures therein for the drainage of wash water, and a pluralityof nested, radially spaced cylindrical drums supported by said ange,said drums having end flanges and intermediate annular ribs to retainseries of pulp mats and pools of stock therein during the rotationthereof and to determine the depth of said pools.

2. Apparatus for purifying "pulp stock, comprislng a vertical rotatableshaft, a conical support member secured at its upper end to said shaftfor rotation therewith and extending downwardly and outwardly, a pair ofnested cylindrical drums supported adjacent to their lower ends by saidsupport member, said drums having end flanges and intermediate annularribs to retain series of pulp mats and overlying pools of stock thereinduring the rotation thereof and to determine the depth of said pools,means for feeding into the several drums at the same end separatestreams of pulp to be purified, and means for co1- lecting the purifiedpulp discharged from the opposite end of the drums.

3. Apparatus for purifying pulp stock, comprising a vertical rotatableshaft, a conical support member secured at its upper end to said shaftand diverging downwardly away from the shaft, a plurality of nestedcylindrical drums supported by the lower end of said member, each saiddrum having an inwardly projecting ange at its upper end and a secondange at its lower end projecting inwardly further toward the axis, meansfor feeding separate streams of pulp into the several drums adjacent tothe lower anges thereof, and means for collecting the pulp dischargedover the upper flanges thereof.

4. Apparatus for purifying pulp stock, comprising a vertical rotatableshaft. a conical support member secured small end uppermost to saidshaft, a plurality of cylindrical drums supported adjacent to theirlower ends by the lower end of said support member, each said drumhaving an inwardly projecting flange at its lower and upper ends andbetween said ends, the inner diameter of the uppermost flange in eachdrum being greater than that of the corresponding lowermost flange,means for feeding separate streams of pulp into the lower ends of theseveral drums, and means for collecting the pulp discharged from theupper ends of said drums.`

5. Apparatus for purifying paper-pulp stock, comprising a plurality ofnested, substantially vertical radially spaced rotatable cylindricaldrum, end members within the upper and lower ends of said drums adaptedto retain pools of pulp-stock within said drums during rotation thereof,the upper end members being formed to provide for the free andunobstructed escape of purified pulp stock over the upper rims of thedrums, the lower end members being formed to provide substantialopenings for the escape of wash water and dirt-retaining fiber when thedrums are stopped and washed, and to prevent downward escape of pulpstock from the drums during operation thereof, and means for supplyingto the several drums separate streams of pulp stock to be purified.

6. Apparatus for purifying paper-pulp stock, comprising a plurality ofnested. radially spaced cylindrical drums rotatable about a commonvertical axis, end members within the upper and lower ends of said drumsadapted to retain therein pools of stock during the operation thereof,said upper end members consisting of rings extending radially inward andterminating in edges forming complete circles concentric with the axisof rotation for the unobstructed discharge of excess pulp stockthereover, said lower end members having substantial openings thereinfor the escape of wash water and dirt-retaining fiber when the drums arestopped and washed, skimming members in said drums, and means forfeeding into the several drums near the lower ends thereof separatestreams of stock to be purified.

RALPH S. CLARKE.

